MIAMI — Tropical storm warnings have been issued for the Southeast coast from north Florida to South Carolina as a cluster of thunderstorms was gathering strength early Saturday and expected to become Tropical Storm Beryl over the Memorial Day weekend.

The National Weather Service said that the storm's maximum sustained winds were at 45 mph. But they are expected to increase as the storm moves over the waters of the Atlantic.

The system was about 285 miles (460 kilometers) from Charleston, S.C., at 2 a.m. and swirling toward the Southeast coast.

Tropical storm warnings were issued for the Volusia/Brevard County line in Florida to Edisto Beach, S.C., and watches from Edisto Beach to the Santee River. The storm is expected to eventually move southwest and the Georgia coast and northern Florida could see heavy rains starting Sunday and into next week.

Higher than normal tides will be crashing against the Southeastern coast and may cause flooding. Heavy rain is forecast and dangerous surf was expected along the coasts of northeastern Florida, Georgia and South Carolina over the holiday weekend.

Forecasters are classifying the storm as Subtropical Storm Beryl, which has more to do with how the center of the storm is forming, not wind speed, according to Weather Underground's website. It is the second named Atlantic storm of the hurricane season that doesn't officially begin until June 1.

Often when subtropical storms remain over warm water for several days, they become tropical because thunderstorms start building close to the center.

Forecasters were not indicating that the storm would become a hurricane.